The invention concerns a key joint for non rotational attachment of an electric rotor to a shaft.
A rotor for a squirrel-cage motor is provided with short-circuit bars around its it periphery. In order to obtain uniform operation of the motor, these bars are preferably somewhat inclined with respect to the shaft direction, meaning that none of the longitudinal grooves in the core discs of the rotor are parallel to the direction of the shaft. The inclination then depends on the number of grooves in the stator circuit, which in its turn depends on the number of poles, the effect of the field and the voltage.
The inclination of the grooves requires that the key joint employed to attach the large rotor to the shaft in a non-rotational manner, also must be inclined with regard to the direction of the shaft. This brings about certain problems. Thus, it may be difficult to obtain an appropriate depth for the keyway, especially at the ends thereof and in addition the great number of variants involved means that many shafts having varying inclinations of the keyway must be manufactured and maintained in stock.
An alternative to using a keyway in the motor shaft would be to attach a key to the shaft by using a fixture. Under these circumstances the key and the shaft are each provided with bores for accepting rivets to achieve final assembly. However, this solution has the disadvantage that a great number of different units or shaft and key combinations must be kept in stock.
In order to secure short delivery times, using known embodiments, ten different shaft units must typically be kept in stock. This of course is very expensive.